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Grafting is an ancient plant propagation technique widely used in horticultural crops, particularly in fruit trees. However, the involvement of two different species in grafting may lead to lack of affinity and severe disorders between the graft components, known as graft-incompatibility. This complex agronomic trait is traditionally classified into two categories: "localized" (weak graft unions with breaks in cambial and vascular continuity at the graft interface and absence of visual symptoms in scion leaves and shoots) and "translocated" (degeneration of the sieve tubes and phloem companion cells at the graft interface causing translocation problems in neighboring tissues, and reddening/yellowing of scion leaves). Over the decades, more attention has been given to the different mechanisms underlying the "localized" type of graft-incompatibility; whereas the phenylpropanoid-derived compounds and the differential gene expression associated with the "translocated" graft-incompatibility remain unstudied. Therefore, the aim of this study was to shed light on the biochemical and molecular mechanisms involved in the typical "translocated" graft-incompatibility of peach/plum graft-combinations. In this study, the "Summergrand" (SG) nectarine cultivar was budded on two plum rootstocks: "Adara" and "Damas GF 1869". "Translocated" symptoms of incompatibility were shown and biochemically characterized in the case of "SG/Damas GF 1869" graft-combination, 3 years after grafting. Non-structural carbohydrates (soluble sugars and starch), phenolic compounds and antioxidant activity, were significantly enhanced in the incompatible graft-combination scion. Similarly, the enzymatic activities of the antioxidant enzyme peroxidase, the phenylalanine ammonia-lyase (PAL) and polyphenol oxidase involved in the phenylpropanoid pathway were significantly affected by the incompatible rootstock "Damas GF 1869", inducing higher activities in the scion than those induced by the compatible rootstock "Adara". In addition, a positive and strong correlation was obtained between total phenol content, antioxidant capacity and the expression of the key genes involved in the phenylpropanoid pathway, PAL1 and PAL2. Regarding the "SG/Adara" graft-combination, there were neither external symptoms of "translocated" incompatibility nor significant differences in the biochemical and molecular parameters between scion and rootstock, proving it to be a compatible combination. The differential expression of PAL genes together with the biochemical factors cited above could be good markers for the "translocated" peach/plum graft-incompatibility. [ABSTRACT FROM AUTHOR]

Graft incompatibility (GI) between the most popular Prunus rootstocks and apricot cultivars is one of the major problems for rootstock usage and improvement. Failure in producing long-leaving healthy grafts greatly affects the range of available Prunus rootstocks for apricot cultivation. Despite recent advances related to the molecular mechanisms of a graft-union formation between rootstock and scion, information on genetic control of this trait in woody plants is essentially missing because of a lack of hybrid crosses, segregating for the trait. In this study, we have employed the next-generation sequencing technology to generate the single-nucleotide polymorphism (SNP) markers and construct parental linkage maps for an apricot F1 population "Moniqui (Mo)" × "Paviot (Pa)" segregating for ability to form successful grafts with universal Prunus rootstock "Marianna 2624". To localize genomic regions associated with this trait, we genotyped 138 individuals from the "Mo × Pa" cross and constructed medium-saturated genetic maps. The female "Mo" and male "Pa" maps were composed of 557 and 501 SNPs and organized in eight linkage groups that covered 780.2 and 690.4 cM of genetic distance, respectively. Parental maps were aligned to the Prunus persica v2.0 genome and revealed a high colinearity with the Prunus reference map. Two-year phenotypic data for characters associated with unsuccessful grafting such as necrotic line (NL), bark and wood discontinuities (BD and WD), and an overall estimate of graft (in)compatibility (GI) were collected for mapping quantitative trait loci (QTLs) on both parental maps. On the map of the graft-compatible parent "Pa", two genomic regions on LG5 (44.9–60.8 cM) and LG8 (33.2–39.2 cM) were associated with graft (in)compatibility characters at different significance level, depending on phenotypic dataset. Of these, the LG8 QTL interval was most consistent between the years and supported by two significant and two putative QTLs. To our best knowledge, this is the first report on QTLs for graft (in)compatibility in woody plants. Results of this work will provide a valuable genomic resource for apricot breeding programs and facilitate future efforts focused on candidate genes discovery for graft (in)compatibility in apricot and other Prunus species. [ABSTRACT FROM AUTHOR]

Abstract: Graft compatibility with at least most commercial cultivars is an essential trait in rootstock breeding programs for orchard performance and longevity. However, its range of application is restricted by physiological and biochemical factors that produce incompatible grafts. As a biological process, the incompatibility reaction is difficult to study because of the wide range of different scion–rootstock interactions produced when grafting. The aim of this study was to characterize the early cellular signs of graft incompatibility based mainly on histochemical tests and the quantification of cell-to-cell communication via plasmodesmata using a novel method termed in vitro ‘stem unions’. Results from different Prunus graft combinations demonstrated that adhesion and callus proliferation occurred in both compatible and incompatible combinations 1 week after grafting. Nevertheless, the new cambium formation derived from the callus tissue appeared to be delayed in incompatible heterografts. A different cell wall composition as well as an enhanced metabolism was detected in the incompatible unions. Using fluorescence redistribution after photobleaching (FRAP) of a symplastic tracer, we determined the plasmodesmal coupling within the tissues primarily involved in the grafting processes. We found that the plasmodesmal coupling was higher between callus cells than between cortex cells. In addition, the plasmodesmal coupling was significantly higher within interfaces from compatible graft combinations compared with that of incompatible unions when analysed 2 weeks after grafting. These new findings strengthen the idea that callus cells are playing a central role in scion/rootstock interaction and that late rejection is predetermined already at the initial steps of union formation. [Copyright &y& Elsevier]

In the last years, an important renewal of plant material from different breeding programs is taking place in apricot in order to improve resistance to biotic stresses, extension of the harvest season, fruit quality, and productivity. However, the graft compatibility of many of these cultivars with most popular Prunus rootstocks is unknown, and this is an essential agronomical trait for their better performance and longevity. Hence, the introduction of new cultivars requires knowledge of the extent and nature of incompatibility reactions before releasing these cultivars on the market. In this study, the determination of graft compatibility was carried out in 13 new apricot cultivars grafted on four Prunus rootstocks: 'Marianna2624' (P. cerasifera × P. musoniana), 'Miragreen' (P. cerasifera × P. davidiana), 'Mirared' (P. cerasifera × Nemared), and 'Montclar' (P. persica L. seedlings) at early stages of development. By combining cytomorphological, anatomical, and phenylalanine ammonia-lyase (PAL) gene expression analysis at the graft interface, as well as different vegetative parameters, the results highlighted 'Miragreen' and 'Mirared' as promising rootstocks for apricot, showing the highest degree of compatibility with more than 90% of the apricot cultivars. These results provide useful information for breeders and growers by selecting the most suitable scion-rootstock for efficient orchard design by planting compatible graft combinations. [ABSTRACT FROM AUTHOR]

In viticulture, grafting is used to propagate Phylloxera-susceptible European grapevines, thereby using resistant American rootstocks. Although scion–rootstock reciprocal signaling is essential for the formation of a proper vascular union and for coordinated growth, our knowledge of graft partner interactions is very limited. In order to elucidate the scale and the content of scion–rootstock metabolic interactions, we profiled the metabolome of eleven graft combination in leaves, stems, and phloem exudate from both above and below the graft union 5–6 months after grafting. We compared the metabolome of scions vs. rootstocks of homografts vs. heterografts and investigated the reciprocal effect of the rootstock on the scion metabolome. This approach revealed that (1) grafting has a minor impact on the metabolome of grafted grapevines when tissues and genotypes were compared, (2) heterografting affects rootstocks more than scions, (3) the presence of a heterologous grafting partner increases defense-related compounds in both scion and rootstocks in shorter and longer distances from the graft, and (4) leaves were revealed as the best tissue to search for grafting-related metabolic markers. These results will provide a valuable metabolomics resource for scion–rootstock interaction studies and will facilitate future efforts on the identification of metabolic markers for important agronomic traits in grafted grapevines. [ABSTRACT FROM AUTHOR]

Grafting is the most used propagation method in viticulture and is the unique control strategy against Phylloxera. Nevertheless, its practice remains limited mainly due to inconsistent graft success and difficulties in predicting graft compatibility responses of proposed scion–rootstock combinations, slowing down the selection of elite rootstocks. Aiming to identify optimal phenotypic parameters related to graft (in)compatibility, we used four clones of two grapevine cultivars that show different compatibility behavior when grafted onto the same rootstock. Several physiological parameters, internal anatomy of the graft union, chlorophyll fluorescence, and pigment contents of homo- and heterografts were monitored in a nursery-grafting context. The measurements highlighted enhanced performance of the heterografts due to rooting difficulties of Vitis vinifera homografts. This suggests that in viticulture, homografts should only be used as compatibility controls regarding qualitative attributes. By observing the internal anatomy of the union, we found that grapevines might require longer times for graft healing than anticipated. While Affinity Coefficients were not informative to assess incompatibility, leaf chlorophyll concentration analysis proved to be a more sensitive indicator of stress than the analysis of chlorophyll fluorescence. Overall, we conclude that graft take correlated best with callus formation at the graft junction three weeks after grafting. [ABSTRACT FROM AUTHOR]

The article describes the Monrepos plum rootstock for cherries. This rootstock was bred at the Agri-Food Research and Technology Center of Aragón (CITA) in Zaragoza, Spain. Furthermore, this rootstock was selected from an open-pollinated population of Myrobolan. An overview of the rootstock's origin and performance is provided.

The graft incompatibility is a problem that causes economic loss to producers and delay in the launch of new cultivars and rootstock because of the long time required for compatibility testing. The aim of this review is to show of the most important and relevant research conducted over the years involving the graft incompatibility in fruit species, specially the genus Prunus. The graft incompatibility is an extremely complex phenomenon that involves anatomical, physiological, biochemical and molecular interactions between scion and rootstock. Being for this reason a difficult problem to analyze. However, it is believed that through a joint analysis of graft incompatibility the understanding of the mechanisms may advance more quickly and so allow the solution for the phenomenon. [ABSTRACT FROM AUTHOR]

• In grapevines grafting became a mechanized procedure due to its unavoidability. • Graft incompatibility is a mystery with unclear definition. • Incompatibility was hypothesized as cell-rejection, metabolic imbalance, immunity. • Nucleic acid trafficking could mediate scion-rootstock communication. • Mobile RNAs, QTLs mapping, metagenomic analysis might unravel incompatibility. Grafting is a method for plant propagation and improvement. In the European viticulture, grafting is the sole control strategy against Phylloxera injuries and thus is of crucial importance for sustainable grape production. Despite its benefits, grafting is also a source for disease dissemination and graft incompatibility sometimes detected long after grafting can result in propagation losses. However, the physiology of grafting, such as compatibility factors, callus formation and healing processes, and the signaling components exchanged between scion and rootstock, are still not well understood by the scientific community. Recent insights in grafting research hint at a complex scion-rootstock communication. Molecules exchanged between rootstock and scion, such as hormones, metabolites, proteins, and RNAs coordinate the grafted plant parts and are suspected to modulate the healing of the union and to facilitate the regeneration of the vascular tissues. Such processes result in a successful grafted plant but in many cases, the graft develops distress symptoms, which can appear in early or late stages of plant growth eventually leading to a so-called 'graft incompatibility'. It is not known whether the cause of incompatibility is based on a rejection of the opposing partners, on growth differences, or on the stress induced by grafting itself. One potential factor leading to graft incompatibility can be based on a deficiency of the recognition of graft-transmissible RNA signals shown to coordinate developmental and environmental shoot-root responses. This review summarizes the current knowledge on grafting from the perspective of viticulture, discusses the hypotheses behind graft incompatibility, addresses the molecular effects of grafting, and novel research perspectives that might help to unveil this millenary mystery. [ABSTRACT FROM AUTHOR]